Hydraulic control systems are used to control the operation of hydraulic actuators such as steering cylinders. A typical hydraulic control system can receive a manual input from an operator, and based on the input can produce a hydraulic response that is correlated with the input. For example, in the case of a hydraulic steering system for a vehicle, the operator may turn a steering wheel which causes the hydraulic system to concurrently actuate a steering cylinder in such a way that the wheels or tracks of the vehicle turn at a rate and degree that correspond to the rate and degree in which the steering wheel is turned. Typically, the manual input provided by the operator causes the displacement (i.e., deflection, movement, etc.) of an actuator control valve which controls hydraulic fluid flow to the hydraulic actuator. In hydraulic systems, the amount of load applied to the hydraulic actuator can alter the way the hydraulic system performs. For example, for certain actuator control valves, the gain rate (e.g., the rate the hydraulic flow changes per incremental movement of the valve) varies based on load. FIG. 1 shows an example gain curve for a typical closed-center steering control unit. As depicted, the valve provides substantially lower gain rates under heavy loads as compared to under light loads.
Hydraulic systems that require human reaction to compensate for load variations can be problematic. For example, a steering system that requires human reaction to compensate for steering load variations caused by ground speed and terrain variations may result in the operator feeling less secure. This can cause a reduction in productivity. To address such a situation, load-sense systems have been developed. Load-sense systems typically control hydraulic pressure and flow so that a given hydraulic system will react the same regardless of load. FIG. 2 illustrates an example gain curve for a typical load-sense steering control unit. As shown, the gain rates are the same regardless of load.